• # question_answer A spherical drop of molten metal of radius 2 mm was found to solidify in 10 seconds. A similar drop of radius 4 mm would solidify in: A) 14.14 second                 B) 20 secondsC) 18.30 second                 D) 40 seconds

Solidification time for a sphere, $t\,\alpha {{\left( \frac{V}{A} \right)}^{2}}$ $\frac{V}{A}=\frac{\left( \frac{4}{3}\pi {{r}^{3}} \right)}{4\pi {{r}^{2}}}=\frac{r}{3}$ $t\propto {{r}^{2}}$ $\frac{{{t}_{2}}}{{{t}_{1}}}={{\left( \frac{4}{3} \right)}^{2}}=4$ ${{t}_{2}}=4\times 10=40s$